Steam propulsion control system



M. M. HOBBS ET AI- STEAM PROPULSION CONTROL SYSTEM Oct. l5, 1968 FiledApril 6, 196e 2 Sheets-Sheet l Oct. l5, 1968 M. M. Hoses ET AL STEAMPROPULSION CONTROL SYST Filed April 6, 196e 2 Sheets-Sheet 2 oon. A?.

bpl H NM] u United States Patent O 3,405,676 STEAM PROPULSION CONTRGLSYSTEM Milton M. Hobbs, Marple Springfield, Pa., and Leaman B.

Podolsky, Wilmington, Del., assgnors to Westinghouse ElectricCorporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Apr.6, 1966, Ser. No. 540,556 14 Claims. (Cl. 11S-.5)

ABSTRACT F THE DISCLOSURE Apparatus disclosed includes a steam turbinedriven reversible ship propulsion system having respective ahead andastern control valves driven by separate servo sys- Items, which are inturn selectively driven by a rproportional plus integral operationalamplier whose input responds to a summation of signals representingactual and desired propeller speeds. Apparatus responsive to onormalconditions, such as low boiler pressure, produce off-normal signalswhich modify the speed control signals applied to the servo systems in amanner to limit the valve openings so that the capability of the systemcannot be exceeded. Means is also provided to restrict the integra-tingcapability of the operational amplifier so that it integrates only whenthe desired speed signal dominates the actual speed signal.

This invention relates to control systems for steam turbines and thelike, and more particularly to a steam -turbine propulsion controlsystem for ships wherein the ship can be controlled directly from thebridge.

In the past, ship propulsion turbines have normally been controlled bysteam valves manually adjusted in the engine room is response to signalsfrom the bridge. For example, if it were ldesired to reverse the shipspropeller from ahead to astern as in docking, an order was transmittedfrom the bridge to the engine room operator who would then manuallyclose the ahead valve and thereafter manually open the astern valve. Inaddition to following commands from the bridge, the engine room operatorhas also been responsible for limiting the propulsion turbines transientste-am requirements to within the capability of the boiler. That is, hehas been responsible for protecting the complete power system fromundesirable modes of operation such as overpressure or underpressureconditions and high or low water levels in the boiler. Needless to say,this method for ship control, While used extensively, leaves much to bedesired particularly as regards the maneuverability of the ship.

As an overall object, the present invention provides an automaticpropulsion control system for ships and the like wherein the shipturbines are controlled `automatically from the bridge, and without theassistance of personnel in the engine room. As will be understood, thisplaces the 'ship under the direct control of the bridge and facilitates'much faster response characteristics in the control of the ship as areneeded, for example, when the ship is being docked.

Another object of the invention is to provide a ship propulsion controlsystem of the type described incorporating means for sensing off-normalconditions or equipment failures, and wherein ott-normal conditions orequipment failures will override the normal automatic function of thesystem and prevent damage to 'any part of the propulsion equipment.

In accordance with the invention, a servo system is provided includingmeans under the control of the bridge for producing a desired speedsignal, means for producing an actual speed signal proportional inmagnitude to the speed of rotation of the ships propeller, apparatus forcomparing the actual and desired speed signals to Patented Oct. 15, 1968produce a speed error signal when the desired and actual speed signalsare not of the same magnitude, and apparatus responsive to the speederror signal for controlling the admis-sion of steam to the shipsturbines. In the ernbodiment of the invention shown herein, -the desiredspeed signal is produced by means of a potentiometer adapted to producea `direct current voltage of one polarity for the ahead direction and adirect current voltage of the opposite polarity for the asterndirection, the magnitude of the voltage being proportional to thedesired speed in either the ahead or astern direction. The actual speedsignal is generated by means of a tachometer generator connected to theships propeller; and the actual and desired speed signals or voltagesare added in series to produce the speed error signal which is appliedthrough operational ampliers to servomotors which control the main aheadand astern steam valves for the ships turbines.

Further, in accordance with the invention, off-normal conditions such aslow boiler pressure are sensed to generate an olf-normal signal whichreduces or limits the steam valve opening when an ott-normal conditionoccurs such that the capability of the system cannot be exceeded. Thus,the system not only provides for normal control of the propulsionsystem, but also eliminates the need for system monitoring by engineroom personnel.

The above and other objects and features of the invention will becomeapparent from the following detailed description taken in connectionwith the accompanying `drawings which form a part of this specication,and in which:

FIGURE 1 is a schematic diagram of the overall propulsion and controlsystem of the invention;

FIG. 2 comprises a detailed schematic diagram of various components ofthe electrical control system shown in FIG. l; and

FIG. 3 is a graph illustrating certain of the control characteristicsofthe system of FIGS. 1 and 2.

General overall descriptionl of systemJ FIG. 1

With reference now to the drawings, and particularly to FIG. 1, a shippropeller 10 is driven through a gear reducer 12 by means of highpressure and low pressure steam turbines 14 and 16, respectively.Turbine 14 is connected to gear reducer 12 and, hence, to the propeller10 through rotatable shaft 18. In a similar manner, the low pressureturbine 16 is connected to the gear reducer 12 through shaft 20 havingconventional reversing turbine blades 22 thereon.

Steam for the turbines 14, 16 and Z2 is supplied by means of a pair ofboilers 24 and 26 connected to a common header 28. From header 28, thesteam can ilow through a main ahead valve 30 to the high pressure sideof turbine 14; thence from the low pressure side of turbine 14 andthrough header 32 to the high pressure side of turbine 16. Finally, the.steam at low pressure passes from the low pressure side of turbine 16through header 34 to a condenser 36. Under the circumstances justdescribed, the ship is moving in the ahead direction. In order toreverse the propeller 10 and cause the ship to move in the asterndirection, the Valve 30 is closed and a main astern val-ve 38 opened,whereupon steam will flow to the reversing blades 22 on shaft 20 andthence through header 34 to the condenser 36. The arrangement justdescribed is, of course, a common and well known marine propulsionsystem. As was explained above, the valves 30 and 38 have, in the past,been controlled manually by the ships engine room operator in responseto signals from the bridge.

While two boilers 24 and 26 are shown in the speciiic example of FIG. 1,it will be understood, of course, that a single boiler could be utilizedif desired, depending upon the requirements of the system. It the Waterlevel in the boilers 24 and 26 should exceed a certain maximum limit,water will pass into the turbines 14 and 16. Conversely, enough Watermust be maintained in the boilers 24 and 26 to prevent them from'burning up. Accordingly, each boiler isy provided with leveltransmitters 40 and 42. The transmitters 40 and 42 may be of the typemanufactured by the Bailey Meter Company and identified as ModelLI-2330B. Essentially, such transmitters are adapted to convert a waterlevel indication into a pneumatic pressure.

Pressures from either of the respective transmitters 40 and 42 are, inturn, applied through a three-way valve 44 to a pneumatic diaphragm 46.The diaphragm 46 for boiler 24, for example, is mechanically connectedto a movable core 4S in a first electromechanical transducer 50. `In asimilar manner, the diaphragm 46 for boiler 26 is mechanically connectedto the movable core 52 for a second electromechanical transducer 54.Each of the transducers 50 and 54 includes a primary winding 56connected across the output of a carrier oscillator 58 such that theoutput signal Iappearing across the secondary winding 60 of eithertransducer is an oscillatory signal having a magnitude and phasedependent upon the position of the movable core 48 or 52, as the casemay be. The signal across winding 60 of transducer 50, for example, isrectified and filtered in demodulator circuit 61. Similarly, the signalacross winding 60 of transducer 54 is rectified and filtered indemodulator circuit 62. The direct current outputs of circuits 61 and 62are applied to an override adjustment circuit 64 Which will produce anoutput whenever the direct current signals at the outputs of circuits 61or 62 exceed a predetermined level.

Thus, if the water level within boiler 24 should move above the maximumpermissible level, the core 48 may move upwardly, for example, to thepoint where the signal applied to override adjustment circuit 64 fromthe demodulator 61 causes an output from circuit 64. Similarly, when thewater level in boiler 24 falls below the minimum desired level, movementof the core 48 downwardly will again cause an output yfrom theoverriding adjustment circuit 64. The operation of transducer 54 andcircuit 62 is the same for boiler 26 and, hence, it can be said thatwhenever the water level within either boiler 24 or 26 rises yabove orbelow predetermined set limits as determined by the override adjustmentcircuit 64, an output signal will be applied to an override controller66.

Reverting again to the boilers 24 and 26, the output pressure from theboilers 24 and 26 in header 28 is sensed by a diaphragm 68 which, inturn, actuates a movable core 70 in a third electromechanical transducer72. The transducer 72, like transducers 50 and 54, is provided with aprimary winding 74 connected across the output of carrier oscillator 58.The transducer 72, however, is provided with two output windings 76 and78. With this arrangement, and assuming that the core 70 moves in onedirection, the magnitude of the signal appearing across one winding 76,for example, will increase while that across the other windingdecreases. Conversely, upon downward movement of the core 70, thereverse situation exists.

The signals appearing across windings 76 and 78 are rectified andfiltered in circuits 80# and 82, respectively, the outputs of thesecircuits being combined and applied to the override adjustment circuit64. Whenever the presvvsure in header 28 falls `below a predeterminedlimit as determined by the override adjustment circuit 64, an outputwill be applied to the override controller 66. Although the overrideadjustment circuit 64 may take various forms, conventionally it willcomprise diodes which are biased in the reverse direction such that theywill conduct to produce an output signal to circuit 66 only when thebias voltage is exceeded. This bias voltage is preferably adjustablesuch that the maximum and minimum pressures, and the upper and lowerlevels of the water within boilers 24 and 26, can be adjusted. Thus, theoverride adjustment circuit 64 will produce an output signal whenever anofi'- saoaeve j normal boiler condition occurs such as reduced pressure,low water level, or high water level. 'Of course, the other off-normalconditions could be utilized to trigger the override adjustment circ-uit64; and, in this respect, the output of the circuit 64 will hereinafterbe referred to in the specification an-d claims as an oit-normal signalwhich is produced when any one of a number of different ofnormalconditions occur;

The main control for the propulsionsystem comprises a throttle controllever 84 movable from acentral or stop position to an ahead positionwhere` the ship moves ahead; and movable backwardly from the stopposition for the astern direction. The throttle lever 84 is connected toa reference divider or potentiometer 88, hereinafter described indetail,such that the output ofthe movable tap on the potentiometer appearingonlead willhave a polarity dependent upon whether the throttle lever 8.4is moved to an ahead position or an astern position, and a magnitudedependent upon the amount of the movement of the throttle lever ineither direction from. its central or stop position. In the particularcontrol system hereinafter described in detail, the output on lead 90will be positive with respect to ground when the throttle lever is movedto an ahead position and negative with respect to ground when it ismoved to an astern position. Further.- more, its magnitude will increasein the positive direction when the throttle lever is moved further in aclockwise direction from the stop position as shown in FIG. l, and willincrease in magnitude in the negative direction as it is moved in acounterclockwise direction from the stop position. The output on lead 90is proportional to desired speed, and its polarity indicative of thedesired direction of movement of the ship. Hence, it will hereinafter bereferred to in the specification and claims as the desired speed signal.

The desired speed signal on lead 90 is added in series with the outputof a tachometer generator 92 mechanically connected to the propeller ithe ship. Hence, the output of the tachometer generator 92 isproportional to the actual speed of the propeller, and the polarityofthe Signal across the output terminals of generator 92 is indicative ofthe direction of actual propeller rotation, either astern or ahead.Hence, the output of tachometer generator 92 will hereinafter bereferred to in the specification and claims as the actual speed signal.

The actual speed signal across tachometer generator 92 normally has apolarity opposing that on lead 90 whenever the lever 84 is moved from apreviously set position. As will be seen, whenever the actual speed ofthe propelr i ler coincides with the desired speed as determined by theposition of throttle lever 84, the output of reference divider 88comprising the desired speed signal will be equal to, and opposite inpolarity to, the actual speed signal produced by the tachometergenerator 92 such that the input to speed control amplifier 94 will bezero. However, whenever the desired speed signal differs from the actualspeed signal, an error signal will be produced which is applied to thespeed control amplifier 94 to vary the steam input to the turbines 14and 16 and thereby adjust the speed of the propeller such that itcoincides with the desired speed.

The speed control amplifier will hereinafter be described in detail;however, for purposes of the present general description, it will besufficient to state that it applies a speed control signal to lead 96which is applied to an ahead servo amplifier 98 as Well as to an asternservo amplifier 100. Whenever an astern control signal appears on lead96, it will be positive with respect'to ground; whereas an ahead controlsignal will be negative With respect to ground.

An output lead 102 from the override controller 66 is connected directlyto the lead 96. The output of the override controller 66 is also appliedto an override inverter 104 via lead 105. It will be noted that the lead102 contains a diode 106 and that the output of the override inverter104 as applied to lead 96 is provided with a diode 108, the diodes 106and 108 being connected in opposing polarity relationship. As willhereinafter be explained, the override Vcontroller 66 and inverter 104comprise, in essence, devices for biasing the diodes 106 and 108 in thereverse direction. Normally, the reverse bias on each diode 106 or 108is about 12 volts; whereas the magnitude of the error signal on lead 96,whether `it be positive or negative, is much less than this.Consequently, under normal conditions, neither one of the diodes 106 nor108 will conduct. However, should an off-normal signal appear at theoutput of circuit`64 due to one of the off-normal conditions heretoforedescribed, the reverse bias on lthe diodes 108 and 106 will be lowered.If, under these conditions, the magnitude o-f'the speed control signalon lead 96 should exceed the reverse bias, the diode 106 or 108 willconduct to effectively bleed off or modify the speed control signal onlead 96 such that its magnitude is limited. For example, if the throttlelever 84 should be rotated in a clockwise direction from the stopposition to the full speed ahead position while the boiler pressure islow, the position of the core 70 in transducer 72 will cause an outputoff-normal signal from circuit 64 which will lower the reverse bias ondiodes 108 and 106. Assuming that the output speed control signal of thespeed control amplifier 94 is larger than the reverse bias on diodes 106and 108, the magnitude of the speed control signal as applied tocircuits 98 and 100 will be limited. This, of course, prevents anyattempts to admit large quantities of steam into the turbines when oneof the aforesaid offnormal conditions occur.

The ahead servo amplifier 98 is part of yan ahead servo motor systemwhich also includes a lirst servo motor 110 coupled to the output ofamplifier 98. The servo motor 110 may comprise a core 112 ofmagnetically permeable material having two windings 114 and 116 thereonand wound in opposite directions. Magnetic fields are appliedtransversely across the ends o'f core 112 by means of C-shaped magnets117 and 119. The output of the ahead servo amplifier 98 is applied tothe windings 114 and 116 in apush-pull arrangement such that when thespeed control signal on lead 96 is negative and increasing in thenegative-direction, the core 112 will be rotated about pivot point 118in one direction. When the signal on lead 96 is negative but decreasing,the corev112 will rotate in the opposite direction. The core 112, inturn, is mechanically coupled to the Valve -30 such that as themagnitude of the negative speed control sign-al on lead 96 increases,the core 112 will rotate in one direction to open valve 30 further;while when the lmagnitude of the negative signal on lead 96 decreases,the core 112 will rotate in the opposite direction to thereby cause thevalve 30 to close further. The core 112 is connected to valve 30 througha `suitable hydro-mechanical servo mechanism, schematically illustratedby broken line 113. When a negative voltage on lead `96 is neitherincreasing nor decreasing, the core 112 and valve 30 will remain intheir previouslyestablished conditions due to the negative feedback path121 around amplifier 98 providing a conventional serv loop.

The astern servo ampli-fier 100 is part of an astern servo motor systemwhich also includes a second servo motor 120 coupled to the output ofamplifier 100. Like motor 110, servo motor 120 has a pair of windings122 and 124 connected in a push-pull arrangement together with a movablecore 126 mechanically connected to the astern valve 38 through asuitable hydroJmechanical servo mech- .anism schematically illustratedby the broken line 127, so as to open or close this valve in response toa positive speed control signal on lead 96. That is, positive controlsignals which are increasing in the positive direction will cause valve38 to open further; While decreasing positive control signals will causethe valve 38 to close. Whenever a positive control signal on lead 96 isnot changing, the valve 38 will remain in its previously establishedposition due to the negative feedback path 127 around amplifierproviding a conventional servo loop. As will be understood, the valves30 and 38 are of the type which can also be operated manually.

The operation of the system of FIG. 1 can be summarized as follows:Assuming, for example, that it is desired to move in the ahead directionfrom a stop position, the throttle lever 84 is rotated in a clockwisedirection, thereby producing a desired speed signal on lead 90. Since,at this particular time, the propeller 10 is not rotating, the voltageacross tachometer generator 92 will be zero, and a speed control signalappears at the output of amplifier 94. This speed control signal will beof negative polarity and of increasing magnitude. Hence, it will actuatethe servo motor through amplifier 98 to open the ahead steam valve 30.Once the voltage at the output of reference divider 88 matches thatproduced by tachometer 92, the voltage on lead 96 of negative polarityremains constant at a fixed level roughly proportional to the desiredspeed setting of the control lever 84. The servo amplifier 98, however,will open the valve 30 only to effect the desired speed setting,whereupon the output of the servo amplier will remain fixed by virtue ofnegative feedback path 121 in accordance with usual practice. Of course,the feedback path 121 can be replaced by a mechanical-type feedbackarrangement connected to the core 112 or other parts of the valve 30.Now, if it is assumed that it is desired to reduce the speed of theship, throttle lever 84 will be rotated in a counterclockwise direction.In this case, the magnitude of the voltage on lead 96 will decrease,whereupon the valve 30 will close further to reduce the amount of steamsupplied to the turbines 14 and 16. The operation for the astern servoamplifier and servo motor is, of course, the same except that in thiscase the polarity of the voltage on lead 96 is positive rather thannegative.

Reference divider With reference now to FIG. 2, the detailed circuitryof the invention is shown. The reference divider 88 comprises a voltagedivider 132 having its center point grounded and its opposite endsconnected to the positive and negative terminals of direct currentvoltage sources, in this case voltage sources of about 24 volts. Variouspoints on the voltage divider 132 are connected to contacts identifiedas 1C through 12C adapted to be engaged by a rotary wiper brush 134which is connected to the throttle lever 84 and rotatable therewith.Wiper brush 134, in turn, is connected to the lead 90. It will beunderstood that as the wiper brush 134 rotates in a counterclockwisedirection from its center or stop position, the voltage on lead 90(i.e., the desired speed signal) will be negative with respect toground. Furthermore, the further the wiperbrush 134 rotates in acounterclockwise direction from its stop position, the greater themagnitude of the negative voltage on lead 90. Conversely, as the wiperbrush 134 rotates in a clockwise direction from its center or stopposition, the voltage or desired speed signal on lead 90` will bepositive with respect to ground and will increase in magnitude as thewiper brush 134 rotates further from its center position. Thus, thereference divider 88 can be positioned at any one of -five ahead speedpositions, five astern speed positions, and a stop position. As will beseen, each throttle switch position provides closure of a number ofindependent circuits which will fulfill all necessary logic andinformation functions associated with the speed throttle and propulsionplant operation. It will be noted, however, that when the wiper brush134 is at the center or stop position, the contact 12C to which it isconnected is not at ground potential (i.e., zero voltage), but rather isconnected through lead 136 to a tap on variable resistor 138 in thevoltage divider 132. Hence, depending upon the position of the movabletap on resistor 138, a slight positive voltage will exist on lead 90,even when the throttle lever 84 is at the center or stop position,

.7 Logic control-transfer between engine room and bridge In order forthe bridge of the ship to assume control of the turbines 14 and 16,certain equipment conditions must first be met. Relay A senses theexistence of these required conditions before permitting control andoperation of the propulsion turbines from the bridge. In this respect,the output of ahead servo amplifier 98 is normally ygrounded throughnormally closed contacts A1 of the relay A. Simila-rly, the output ofthe astern servo amplifier 100is normally-grounded throughl normallyclosed contacts A2 of the relay A. Hence, as long as the relay A is notenergized, the valves 30 and 38 cannot be controlledby the throttlelever 84 directly from the bridge.

Control'may be transferred from the engine room to the bridge only whenal master switch 140` is closed and certain Vother conditions are met.These certain other conditions are represented in FIG. 2 by the logiccircuit 142 which, in essence, comprises a plurality of contacts, all ofwhich must be closed to complete a circuit to the relay A upon closureof switch 140 before the relay can become energized. However, once relayA becomes energized, it is maintained energized by its own contacts A3until the switch 140 is opened. The switches which are closed tocom-plete the circuit through the logic circuit 142 need not bedescribed herein in detail. It will be sufficient to state that when allof the necessary conditions for bridge control are met, the contactswithin circuit 142 will close to thereby initially energize relay A andpermit bridge control to take over.

Reverting again to the throttle lever 84, it is provided with additionalwiper brushes 148 and 150 which rotate with the wiper brush 134. Withthe throttle lever 84 in its central or stop position, wiper brush 148will act to energize a relay F; and, assuming that contacts H1 and I1are closed, it will also energize relay C. Relay contacts H1 and I1 areon relays H and I, respectively, which relays are energized by closureof limit `switches 152 and 154 respectively, Limit switch 152 is closedwhen the ahead valve 30 is completely closed; whereas limit switch 154is cl-osed when the astern valve 38 is completely closed. It can beseen, therefore, that the relay C will become energized only when thethrottle lever 84 is at its center or stop position and both the aheadand the astern valves 30 and 38 are closed. Once the relay C becomesenergized, it will remain energized through contacts C1, just so long asthe astern valves 38 remains closed and the contacts I1 are closed. Theoverall effect of this is that once the relay C is energized, it willremain energized even through the ahead valve 30 is opened.

' When the throttle lever 84 is moved counterclockwise to an asternposition, the wiper brush 148 will engage arcuate contact 156 to therebyenergize relay B. Hence, relay B will be energized whenever the throttlelever is in -an astern position. Finally, the wiper brush 150 willengage contact -point 158 to energize relay E only when the throttlelever 84 is in its maximum astern position (i.e., on contact 5C). At allother times, the relay E is deenergized.

Speed control amplier The output of the tachometer generator 92 isconnected to ground through two parallel current paths, each of whichincludes three diodes 144-146 connected to conduct current in oppositedirections. The purpose of these diodes is to clamp the speed errorsignal at the output of the tachometer 92 such that it will not exceedthe capabilities of the system. Assume, for example, that the throttlelever 84 is suddenly moved from the stop position to contact 7C (i.e.,maximum speed ahead). Under these conditions, the signal on lead 90 willapproach plus 24 volts; and since the output of the tachometer 92 isessentially zero at this time, a voltage of almost 24 volts, asattenuated by resistor 91 and tachometer 92, would be applied to theinput of the speed control amplifier 94 exceeding the system capability.Accordingly, the clamp comprising the diodes 144 and 146 clamps theoutput from the wiper brush 134 and tachometer 92 to plus4 .or minusabout 1.8 volts. This is well within theI capability of the speedcontrol amplifier 94. Of course, as the speed of of the propeller isgradually brought up to maximum speed ahead, the voltage generated bythe tachometerr'92 will gradually approach that on the wiperbrush 134until the two are equal and the input to the speed control amplifier `94is zero.

The lspeed error signal at the output o f tachometer 92, as clamped bythe diodes 144 and 146 is .applied across a voltage divider in amplifier9'4 comprising three resistors 160, 162 and` 164 connected in series.Resistor 162 is provided with a variable tap whichyis`- connectedthrough a fixed resistor 166 tothe input of an operationalamplifier-168. A capacitor 170'is connected inshunt with the operationalamplifier 168 to lter ripple outof the tachometer generator output. T'he output of1vtheopera tional amplifieris applied through a resistor172 ,tothe lead 96 and hence. to the ahead ser-vo amplifier 98and asternservo amplifier 100. v 1 i Thev operational amplifier arrangement inspeed controller 94 acts as a proportional; plus integral controller;and in this respect it is providedv with a first feedback path`including resistor 174 and capacitor 176 in series. The output of thecontroller for a step input error signal will appear as in FIG. 3. Thus,when the input errorsignal to the amplifier `94 changes abruptlyaboutzero as when wiper brush 134 is moved from contact 12C to contact11C, the output will also change abruptly at time t1 lowering thevoltage at the output of a-mplifier 168 by the amount equal `toV1.`However, yafter this initial step or proportional output, theamplifier will integrate. between the times t1 and t2, thereby changingthe output voltage by an amount equal to V2, but over a longer period oftime. Thus, assuming that the propeller speed has reached equilibriumwith the throttle settingiand that the throttle lever 84 is moved fromone contact point to the next, steam valve 30 will open abruptly duringthe proportional step function operation of amplifier 168 and thereafteropen `relatively slowly between the times -tl and t2. The proportionalcontrol feature is,1of course, neces'- sary to give the ship initialfast response characteristics as are necessary, for example, duringdocking;

In shunt with the capacitor 176 is a first current path including diode178, normally closed contacts F1 of the relay F and normally closedcontacts B1 of relay B. A second current path in shunt with thecapacitor 176 includes a second diode and normally open contacts B2 ofthe relay B. As was mentioned above, when the ship is moving in theahead direction, the output voltage on lead 96 as applied to the servoamplifiers 98 and 100 will be negative with respect to ground; whereasit will be positive with respect to ground when the ship is moving inthe astern direction. When the throttle lever 84 is in an aheadposition, neither of the relays B nor F will be energized. Consequently,current can flow through diode 178, assuming that its anode (i.e., lead96) is positive with respect to its cathode. It may happen that when thethrottle lever 84 is rotated in a counterclockwise direction to producea lower desired speedsignal on lead 90 the output of tachometer willoverrun the desired speed signal until the ship slows down to the pointwhere the speed is again at the desired speed. Under these conditions,and assuming that the diode 178 was not included in the circuit, theoperational amplifier 168 would integrate into the opposite region whenthe speed of the propeller exceeds the desired speed. That is, thecapacitor 176 would charge in the opposite direction; and if it werethen desired to again increase the speed of the ship in the aheaddirection, an unreasonable amount of delay` time would be involved.This, however, is prevented by means of the diode 178. If the throttlelever 84 is at its center or stop position, relay F becomes energized,contacts F1 open, and diode 178 is no longer effective, v

The diode 180 functions in a similar manner, except that it is operativeby virtue of closurevof contacts B2 only when the throttle lever is inan astern position such that the voltage on lead 96 is positive withrespect to ground. During this time, contacts B1 are open to disablethediode 178.

Rate adjustment potentiometers The rate at which the ahead valve 30opens or closes is adjusted by means of a pair of potentiometers 182 and184."The potentiometer 182, for example, is connected in: series withresistor 186 between ground and a source of positive potential.Similarly, the potentiometer 184 is connected inseries with resistor 188between ground and a source of i negative potential. The movable tap onpotentiometer 182 is connected through diode 192 and normally closedcontacts B3-of relay B to the junction of resistors 160 and 162 at theinput to the speed control amplifier 160. Likewise, the'movable tap 'onpotentiometer '184 is connected through diode 194,' normally closedcontacts F2 of'relay F and normally closed contacts B4 of relay B to thejunction of resistors 160 and 162. If the throttle lever 84 is rotatedto the ahead position, the relays B and F will be deenergized.Consequently, the relay contacts B3, B4 an-d F2 will also be closed. Ifthe signal input to the speed control amplifier 94 should exceed thebias on diode 192 when the throttle lever 84 is in an ahead position andthe voltage input to the amplifier 94 negative, the diode -192 willserve to limit the magnitude of the input' signal to the amplifier 94and, hence, the rate at which the ahead valve 30 is closed. Similarly,with the throttle lever 84 in an ahead position and assuming that theinput to'amplifier 9'4 is positive, diode 194 will serve to limit themagnitude of the'input to amplifieri94 as' determined by the lbiasvoltage established by the settingof 'the movable tapon` potentiometer184. This limits the rate at which' the ahead valve is opened.

The rate of opening of the astern valve 38 is controlled `by`rneans'of'a similar arrangement including potentiometers 196 and 198,these potentiometers being con-v nected in series withresistors 200 and202,'respectively'. The movable tapon"potentior`neter -196 is adaptedfor connection to the inputk to amplifier 94 through diode 204,normally'closed contacts E1 of relay E, and either "normally opencontacts B5 of relay B or normally open contacts F3 of relay F. Themovable tap on potentiometer 198 is ada-pted for connection to the inputto operational amplifier 94 through diode 206, normally closedcontactsE2 of relay E and normally open contacts B6 of relay B.

When' the throttle lever 84 is lin an astern position, the contacts B5will be closed as will contactsv E1, assuming thatA the lever is not inthe maximum astern position. Similarly, contacts B6 and E2 .will beclosed. Hence, the diodes204 and 206 will limit'the negative andpositive input signals to amplifier 94 and, hence, the rate of openingor closing of valve 38. Relay contacts E1 and E2 are provided in thesystem for the reason that when the throttle lever is moved t0 themaximum astern position, it is usually in an effort to prevent acollision. For this reason, -no limit is `imposed on the rate of:opening of the astern valve 38 when the throttlelever is in the extremeastern position. Relay contacts F3 are included in the circuit' since ifthe throttle lever is moved from an astern position to a stop position,for example, the astern valve may still be closing and the previouslyestablished limit will still be in effect.

.Interlocking of servo amplifiers With referencel to the servoamplifiers 98 and 100, it will be noted that in addition to contacts A1and A2, a

- number of other contacts are provided for grounding the v output ofthe servo amplifiers to prevent operation of the and 4theahead valvecannot be opened. A similar arrangement is provided for servo amplifierwherein contacts H2, which are normally closed, are in that positionwhen valve`30 is open to prevent opening of the astern valve 38. In thismanner, it will be appreciated that both valves 30 and 38 cannot fbeopen at the same time. The ahead servo amplifier 98 is provided withnormally open relay contacts B7 which close only when the throttle lever84 is in an astern position. Thus, the valve 30 cannot open when thekthrottle lever 84 is in an astern position. Similarly, when the throttlelever lis in an ahead position, contacts B8 for servo amplifier 100 willclose, thereby preventing opening of the astern valve 38, even thoughrelay F is energized to open contacts F4 and relay C is deenergized suchthat contactsCZ` are open. This condition will occurwhen the throttlelever is at its central or .stop position and the astern valve is open.

Override controller With reference now to the override controller 66, itcomprises an operational amplifier 208 which operates as a proportionalamplifier with a time constant. Normally, the output of the operationalamplifier is set at about minus 12 volts as by means of a potentiometer210 oonnected between ground and a source of positive potential, themov-able tap on the potentiometer 210 being connected to the input ofthe amplifier 208 through resistor 212. The amplifier 208 is providedwith twfo feedback paths, one of which includes a diode 214 and theother of which includes a resistor 216 and capacitor 218 'in parallel,these latter circuit elements acting as a filter. The override errorsignal from the override adjustment Icircuit 64 is applied to 'the inputof the amplifier 208 through a resistor 220, the arrangement being suchthat the override signal, being of negative polarity, will reduce themagnitude lof the negative output signal of the operational amplifier208. This reduction in the output from the operational amplifier 208reduces the bias on diode 106.

The output of the operational amplifier 208 is applied to the input ofan operational amplifier 222 in the override inverter 104 through aresistor 224. A bias may be applied to the amplifier 222 by means ofpotentiometer 226 having its movable tap also connected to the inputl ofamplifier 222 through resistor 228. Amplifier 222, like amplifier 208,is provided with two feedback paths one of which includes a diode 230rand the other of which includes a resistor 232. The output from theamplifier 222 will be a positive voltage lof magnitude equal to thenegative voltage at the output of amplifier 208 plus any bias voltageapplied to resistor 226. The output of amplifier 208, in turn, serves tobias the diode 108 in the reverse direction.

The operation of the override controller can perhaps best be understoodby reference to FIG. 3. Thus, the normal bias on the diodes 106 and 108is minus 12 volts and plus 12 volts, respectively, as represented by thelines 234 and 236. Should the control signal applied to the `a conditionmight occur, for example, because of low bo'iler pressure. Under thesecircumstances, the magnitude of the control signal applied to the servoamplifiers 98 and 100 is limited to plus or minus 8 volts. Hence, theopening of valves 30 and 38 is also limited.

Roll-over circuit AWhen the throttle lever 84 is at its central or stopposition and the ship is at rest, it is necessary for the turbines 14and 16 to be started and stopped every few minutes in order that rotorstraightness can be maintained. That is, due to uneven heating of theturbines, the rotorsy will become warped if they are notrotated fromtime-to-time. Therefore, a roll-over control is provided in conjunctionwith the normal control circuitry heretofore described in order torotate the turbines from timeto-time. V

When the throttle lever 84 is at its central position and the asternvalve 38 and ahead valve 30 are both closed, the relays H and I willbecome energized. This closes the contacts H1 and I1 to energize relayC. When relay C becomes energized, relay contacts `C3) in the speedcontrol amplier 94 are closed and relay contacts C4 open. Closure ofcontacts C3 shorts the capacitor 176 and insures that when throttlelever 84 is again moved from its central or stop position, no residualcharge will exist on the capacitor 176. Opening of the contacts C4, ofcourse, prevents normal operation of amplifier 168 since the feedbackpath containing capacitor 176 is now interrupted. When relay C becomesenergized, it opens contacts C5 and closes contacts C6. A secondfeedback path 242 is now connected between the input and output ofamplifier 168. j

As was mentioned above, when the throttle lever 84 is in its central orstop position, a slight positive voltage will appear on lead 90 byvirtue of the fact that contact 12C is connected to the ymovable tap onvariable resistor 138. Feedback path 242 is a high gain feedback circuitcapable of providing a roll-over or intermittent pulsing of the aheadvalve 30. That is, by the action of the circuit, the valve 30 is openedjust long enough for the propeller to be accelerated to some value lessthan 3 revolutions per minute. At this point, the speed is sensed by thetachometer 92 to counteract with a light positive voltage on lead 90,and the speed controller output on lead 96 quickly changes from aboutminus 1 to minus 2 volts necessary for just opening the ahead valve, tothe maximum positive voltage permitted by the |override inverter causing4a hard closing ofthe ahead valve. If the ship has no headway, theturbine speed will gradually reduce to zero and the speed controllerwill begin to integrate from the positive hard closed region back intothe negative region necessary for the next rollaover pulse. This isachieved by means of capacitor 243 in series with resistors 244 'and 246in feedback path 242. The roll-over repetition rate is adjusted byvariable resistor 1 38. The roll-over circuitry per se is the subject ofcopending appli-cation Ser. No. 540,567, filed concurrently herewith andassigned to the assignee vof the present application.

While the invention has been shown in connection with a certain specificembodiment, it will be readily apparent to those skilled in the art thatvarious changes in form and arrangement of parts may be made to suitrequire- `ments without departing from the spirit and scope of theinvention.

We clgim as our invention:

1. In a speed control system for a Huid-driven ship propulsion turbine,the combination of means for producing a desired propeller speed signal,means for producing an actual propeller speed signal, means forcomparing the desired and actual speed signals to derive a speed errorsignal when the desired and actual speed signals differ, valve means forcontrolling the admission of fluid under pressure to said turbine, servomotor means for actuating said valve means, and apparatus includingintegrating lmeans responsive to said speed error signal for drivingsaid servo motor means to adjust the valve means in response to a speederror signal, said integrating means being operative to integrate whenthe desired speed signal dominates the actual speed signal andinoperative to integrate when the actual speed signal dominates thedesired speed signal.

2. In speed control apparatus for a ship propulsion system including amain ahead valve for admitting Huid under pressure to turbine means torotate the ships propeller in one direction and a main astern valve foradmitting fluid under pressure to said turbine means to rotate the shipspropeller in the opposite direction; the combination of ahead servomotor means for actuating the main ahead valve, astern servo mot-ormeans for actuating the main astern valve, -means for producing adesired propeller speedsignal having a rst characteristic indicative ofthe desired direction of movement and a second characteristic indicativeof the desired speed in either direction, means for producing an actualpropeller speed signal having a first characteristic indicative of theactual direction of movement of the ship. and a second characteristicindicative ofthe actual speed of the propeller. in `the desireddirection, means for comparing the desiredandfactual speed signals toproduce a speed error signal when the desired and actual speed signalsdiffer,I means including integrating means responsive to saidspeed-error signal for producing a direct current control voltage whichhas one polarity when the characteristics of the desired speed sign-aldictate an ahead direction and the opposite polarity when thecharacteristics of the desired speed signal dict-ate an asterndirection, said integrating means being operative to integrate when theerror signal is in the same direction as the desired speed signal, meansfor rendering the integrating means inoperative to integrate `.when theerror signal is in the same direction as the actual speed signal, servoamplifier means responsive to said direct current control voltage forcausing the ahead servo motor means to actuate the main ahead valve whenthe direct current control voltage is of one polarity, and servoamplifier means responsive to said direct current control voltage forcausing the astern servo motor means to actuate the main astern valvewhen the direct current control volt-age is of the opposite polarity. l'

n 3. In speed control apparatus `for a ship propulsion system includinga main ahead valve -for admitting fluid under pressure to turbinemeansto rotate ther-ships propeller in one direction and a main asternvalve for admitting fluid under pressure to said turbine means torot-ate the ships propeller in the opposite direction; the combinationof ahead servo motor means for actuating the main ahead valve, asternservo motor means for actuating the main astern valve, :means forproducing a desired propeller speed signal having a first characteristicindicative of the desired direction of movement and a secondcharacteristic indicative of the desired speed in either direction,means for producing an actual propeller speed signal having a firstcharacteristic indicative of the actual direction of movement of theship and a second characteristic indicative of the actual speed of thepropeller in the desired direction, -means for comparing the desired andactual speed signals to produce a speed error signal when the desiredand actual speed signals differ, means responsive to said speed errorsignal for producing a direct current control voltage which has onepolarity when the characteristics ofthe desired speed signal dictate anahead direction and the opposite polarity when the characteristics ofthe desired speed signal dictate an astern direction, servo amplifiermeans responsive to said direct current control voltage for driving theahead servo motor means to actuate the main ahead valve when the directcurrent control voltage is of one polarity, servo `amplifier meansresponsive to said direct current control volt-age for driving theastern servo motor means to actuate the main astern valve when thedirect current control voltage is of the opposite polarity, means forpreventing opening of the astern valve when the ahead valve is open, andmeans for preventing opening of the ahead valve when the astern valve isopen. j

4. In speed control apparatus for a ship propulsion system including amain ahead valve for admitting fluid under pressure to turbine means to'rotate the ships propeller in one direction and a main astern valve foradmitting uid under pressure to said turbine means to rotate the shipspropeller -in the opposite direction; the combination of ahead servomotor means for yactuating the main ahead valve, astern servo motormeans for 13 actuating the mai-n astern valve, means for producing adesired propeller speed signal having a first characteristicindicativeof the'desired direction of movement and a secondcharacteristic indicative of the desired speed in either direction,means for producing an actual propeller -speed signal having a firstcharacteristic indicative of the actual direction of movement of theship and a second characteristicindicative of the actual speed of thepropeller in the desired direction, means for comparing the desired andactual speed signals to produce a speed error 'signal When-the desiredand actual speed signals differ, meansy responsive to said speed errorsignal for producing `a direct Icurrent control -voltage which has onepolarity ywhenithe characteristics of the desired speed signal dictateanahead-direction and the opposite polarity when the characteristics ofthe desired speed signal dictate an astern .dire'ctionfservo amplifiermeans responsive to said direct currenticontrol voltage for causing saidahead servo motor imeans Ato actuate the main ahead valve when thedirect current control voltage is offone polarity, servo amplifier meansresponsive to said direct current control voltage for causing the4astern servo motor means to actuate the main direction.

V5. In a speed control system for a fluid-driven ship propulsionturbine, the combination of means for produc- 'ing a desired propellerspeed signal, means for producing an actual propeller speed signal,means for comparing the desired and actual speed signals to derive aspeed error signal when the desired and actual speed signals differ,valve means for controlling the admission of fluid under pressure tosaid turbine, servo motor means for actuating said valve means,lapparatus including integrating means responsive to said speed errorsignal for driving said servo motormeans to adjust vthe valve means inre- .sponse to a speed error signal, said apparatus for drivingY-theJservo motor means having an output supplying a direct currentcontrol voltage to said servo motor means,

circuit means including reverse-biased diodes Aconnected v to the outputof said apparatus for limiting the magnitude of said direct currentcontrol voltage as applied to the servo motor means, and means forlowering the bias on said diodes in response to the occurrence of anoff-normal condition in Ithe propulsion system for said ship whereby themaximum magnitude of the direct current control voltage as applied tothe servo motor means is correspond- `ingly lowered.-

6. The vcon-trol system of claim 5 including electromechanicaltransducer means for sensing an off-normal condition in the propulsionsystem of said ship, la source of oscillatoryvolt-age for energizingsaid electromechanical transduce-r means, means for rect-ifying theoutput of said electromechanical transducer means, land means includingan opera-t-ional amplifier operable in response to the rectified outputof the transducer means for regulating the reverse bias on said diodes.

7. The control system of claim 5 wherein there are two reverse-biaseddiodes connected to the output of said apparatus, a first of said diodeshaving its cathode connected to the output of said apparatus and asecond of the diodes having its anode connected to the output of saidapparatus, a first operational amplifier having its output connected tothe anode of said first diode, a second Operational amplifier having itsoutput connected to the cathode of said second diode, means forproducing an off-normal signal when an off-normal condition occurs inthe propulsion system of saidship, means for applying said ofinormalsignal to the input o-f said first operational -amplifier, Vand meansfor applying the output of said first 14 operational amplifier to theinput of said second operational amplifier.

8. In a speed control system for a fluid-driven ship propulsion turbine,the combinationof means for producing a desired propeller speed signal,means for producing an actual propeller speed signal, means forcomparing the desired and actual speed signals to derive a speed errorsignal when the desired and actual speed signals differ, valve means forcontrolling the admission of fluid under pressure to said turbine, servomotor means for actuating said valve means, and apparatus responsive tosaid speed error signal for driving said servo motor means to adjust thevalve means in 'response to a speed error signal, said apparatuscomprising an operational amplifier having -a negative feedback pathincluding a resistor and a capacitor in series whereby the output of theoperational amplifier in response to a step input will bea proportionalstep output followed by an integrating output.

9. The control system ofclaim 8 wherein the desired speed signalcomprises a direct current voltage the magnitude and polarity of whichare varied manually under the control of the bridge of the ship, theactual speed signal 4comprises a direct current voltage generated by atachometer generator mechanically coupled to the ships propel- 1er, andmeans for adding said desired and actual speed signals in series toproduce a direct current voltage comprising said speed error signal.

10. The combination of claim 8 wherein said capacitor is shunted by -aunidirectional device poled in the direction of negative feedbackoccurring when said error signal is in the same direction as the actualspeed signal.

11. In speed control apparatus for a ship propulsion system including amain ahead valve for admitting fluid under pressure to turbine means torotate the ships propeller in one direction and a main astern valve foradmitting fluid under pressure to said turbine means to rotate the shipspropeller in the opposite direction; the combination of ahead servomotor means for actuating the main ahead valve, astern servo motor4means for actuating the main astern valve, means for producing adesired propeller speed signal having a first characteristic indicativeof the desired direction of movement and a second characteristicindicative of the desired speed in either direction, means for producingan actual propeller speed signal having a first characteristicindicative of the actual direction of movement of the ship and a secondcharacteristic indicative of the actual speed of the propeller in thedesired direction, means for comparing the desired and actual speedsignals to produce a speed error signal when the desired and actualspeed signals differ, means including integrating means responsive tosaid speed error signal for producing a direct current control voltagewhich has one polarity When the characteristics of the desired speedsignal dictate an ahead direction and the opposite polarity when thecharacteristics of the desired speed signal dictate an astern direction,servo amplifier means responsive to said direct current control voltagefor causing the ahead servo motor means to actuate the main ahead valvewhen the direct current control voltage is of said one polarity, directcurrent control voltage of said one polarity and increasing magnitudecausing said main ahead valve to open, direct current control voltage ofsaid one polarity but of decreasing magnitude causing said main aheadvalve to close, and servo amplifier means responsive to said directcurrent control voltage for causing the astern servo motor means toactuate the main astern valve when the direct current control voltage isof said opposite polarity, direct current control voltage of saidopposite polarity and increasing magnitude causing said main asternvalve to open, and direct current control voltage of said oppositepolarity but of decreasing magnitude causing said main astern valve toclose.

12. In a speed control system for a fluid-driven ship propulsionturbine, the combination of:

(a) means for producing a desired propeller speed signal comprisingvoltage divider Imeans connected between the output terminals of asource of direct current voltage and having an intermediate grounded tapand a plurality of contact points on both sides of the tap, whereby thevoltage on contact points on one side of the tap will be positive withrespect to ground and the voltage on Contact points on the other side ofthe tap will be negative with respect to ground, and a wiper brushengageable with said contact points in succession whereby the voltageappearing between said Wiper brush and ground will cornprise saiddesired speed signal, the magnitude and polarity of the desired speedsignal being dependent upon the contact point which the wiper brushengases;

(b) means for producing an actual propeller speed signal, said actualspeed signal comprising a direct current voltage; and said means forproducing said actual speed signal comprising tachometer generator meansmechanically coupled to the ships propeller, said tachometer generatormeans having rst and second output terminals;

(c) error generating means for comparing the desired and actual speedsignals to derive a speed error signal when the desired and actual speedsignals differ, said error generating means comprising means co-nnectingsaid wiper brush to one of said tachometer generator terminals, andcircuit means including resistance -means connecting the other of saidtachometer generator terminals through said resistance means to ground,said circuit means having a circuit point, at least a portion of saidresistance means being included between said circuit point and ground;whereby said circuit point provides a voltage representing said error;

(d) valve means for controlling the admission of fluid under pressure tosaid turbine;

(e) servo motor means for actuating said valve means;

(f) apparatus including integrating means responsive to said speed errorsignal for driving said servo m0- tor means to adjust the valve means inresponse to a speed error signal, said apparatus having input meansconnected to said circuit point; and

(g) first unidirectional current means for conducting current from saidother terminal of the tachometer generator means to ground in onedirection, and second unidirectional current means connected to saidother terminal of the tachometer generator means for conducting currentto ground in the other direction, said irst and second unidirectionalcurrent means serving to limit the magnitude of the error signal appliedto said apparatus for driving the servo motor means.

13. In speed control apparatus for a ship propulsion system including amain ahead valve for admitting uid under pressure to turbine means torotate the ships propeller in one direction and a main astern valve foradmitting iluid under pressure to said turbine means to rotate the shipspropeller in the opposite direction; the combination of ahead servomotor means for actuating the main ahead valve, astern servo motor meansyfor actuating the main astern valve, means for producing a desiredpropeller speed signal having a first characteristic indicative of thedesired direction of movement and a second characteristic indicative ofthe desired speed in either direction, meansl for producing an actualpropeller speed signal having a first characteristic indicative" oftheactual direction of movement of the'ship and a second characteristicindicative of the actual speedv of the'propeller in the desireddirection, means for comparing the desired and actual speed signals toproduce aspeed error signal when the desired and actual speed signalsvdiier, means including an operational amplifier responsivetto said speederror signal for producing a directcurrent control voltage which has onepolarity when' thercharacteristics of the desired speed signal dictatean lahead direction and the opposite polarity when the characteristicsof the desired speed signal dictate an asterny direction, saidoperational amplifier havingra negative feedback circuit including inseries a resistor and acapacitor, means for unidirectionally shuntingthe capacitor in the same direction as that of the negative feedbackthat occurs when the actual speed signal dominates the desired speedsignal, servo amplifier means responsive to saiddirect current controlvoltage for causing the ahead servo motor means to actuate the mainahead valve when the vdirect current control voltage is of said onepolarity, and

servo amplier means responsive to said direct current control voltagefor causing the astem servo motor means to actuate the main astern valvewhen the direct current control voltage is of said opposite polarity. Y

14. The combination of claim 11 whereinrsaid means responsive to saidspeed error signal includes proportional plus integral controller means.r l l References Cited UNITED STATES PATENTS OTHER REFERENCESStillwagon, R. E.: Central Engine-Room Control for Cargo Ships inWestinghouse Engineer, vol. 24, No. 3, pp. 86-89, May 1964.

ANDREW H. FARRELL, Primary Examiner.

